I know someone who was visited by FBI at their workplace, and at home, because of what they said on a message board. They speculated about how a terrorist attack _could_ happen.

Then there is the recent case of Yasir Afifi. FBI were tracking him because his friend made a post that caught their attention.

Unfortunately our law enforcement and other government agencies don't interpret "freedom of speech" like most regular citizens do. And it certainly doesn't guarantee protections against harassment and embarrassing bullying that accompanies such "investigations"